How to Make Landslides Less Deadly

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CreditJustin Gabbard

By David R. Montgomery and Joseph Wartman

March 20, 2015

SEATTLE — IN the year since 43 people died in a landslide in Oso, Wash., we have often been asked, as researchers who investigated this tragedy, how many other potential landslide disasters exist around the country.

Geologists and engineers certainly have the capability to find out. But the technological tools developed over the past several decades have not yet been put to work to develop detailed, reliable maps of landslide hazards nationwide. So no one really knows the answer.

The Oso disaster was one of the deadliest single landslides in recent history. After several weeks of heavy rainfall, roughly 10 million cubic yards of sand, gravel and mud cascaded down the side of a valley and surged across the valley bottom, destroying a residential community. Though the consequences of the Oso slide were particularly devastating, the United States Geological Survey has estimated that, on average, landslides kill 25 to 50 people a year in the United States, though typically in smaller events that attract less media attention.

Landslides occur in all 50 states — even the relatively flat ones. But they plague mountainous regions in California, Colorado and the Pacific Northwest, and are common throughout Appalachia and New England.

Often set off by heavy rains or earthquakes, landslides may strike suddenly, but they are hardly random. Geologists can identify landslide-prone slopes, even if it is more difficult to predict when they will fail and how far they will travel when they do.

Over the past decade, the science of landslide mapping has advanced rapidly, largely because of improvements in remote sensing technologies that allow us to see Earth’s surface in unprecedented detail. Today, it would be possible to create high-resolution hazard maps for the entire nation for significantly less than the estimated $1 billion or more in losses that landslides cause each year in the United States.

These high-resolution maps are available in other countries, including New Zealand, Italy and Switzerland, where they provide valuable information to citizens and public officials about risks. They guide land-use policy and allow people to make informed decisions before buying or building a home.

In the United States, however, few landslide hazard maps include quantitative estimates of the likelihood of landslides. State and local mapping programs have been hampered by a lack of money and, in some cases, politics. Concern about the impact of mapping on development was among the factors that led the North Carolina Legislature to shut down a hazard-mapping initiative in 2011. The effort was begun in 2004 after landslides killed five people in the state.

You don’t need to be a geologist to understand that these hazard maps should identify where landslides have happened, where new ones are likely to occur and how much land they may overrun. Yet few landslide hazard assessments cover all of those bases.

Consider, for example, the case of the nurse who bought her dream house just days before she died in the Oso slide. Hazard maps identified the steep slope across the river from her home as a landslide zone. But the flat land where she had just moved was not described as at risk. How could she have known that she was moving into harm’s way?

A decade ago, the National Research Council, an arm of the National Academies that provides advice on science and technology, recommended a major national landslide assessment program that would have included money for state geological surveys to evaluate or re-evaluate landslide hazards using modern technologies. The council’s study estimated that the effort would cost $20 million in the initial stages of a 10-year program and up to $50 million a year in the final three years.

However, the program never materialized, and annual financing for the Geological Survey to research and evaluate hazards has remained essentially flat over the last decade when adjusted for inflation. The current budget for the program is $3.5 million.

Few homeowners have the expertise to realistically assess landslide hazards themselves, and even if they did, landslide insurance is not commonly available. With extreme weather events expected to become increasingly common, we need to commit to a program to systematically map landslide hazards across the nation and use that information to reduce landslide risks.

Millions of us live, work and play on or below slopes that may one day turn against us. But until we begin to better identify, map and mitigate the risks, we can expect landslides to continue to exact a toll in human lives.

David R. Montgomery is a professor of earth and space sciences, and Joseph Wartman is an associate professor of civil and environmental engineering, at the University of Washington.

A version of this article appears in print on , on Page A19 of the New York edition with the headline: How to Make Landslides Less Deadly. Order Reprints | Today’s Paper | Subscribe